Questions tagged [speed-of-light]

The speed of light is a fundamental universal constant that marks the maximum speed at which energy and information can propagate. Its value is $299792458\frac{\mathrm{m}}{\mathrm{s}}$.

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48 views

Does light comeback again?

I know light follow the space time curvature.I listen about gravity lensing.Is there any proof of total reflection of light due to gravity like total internal reflection of light? If this possible ...
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Relativistic mass of particles

My question is about aquiring mass by particles moving at speeds comparable with $c$. Is this somehow related to the logic that a force field that is moving in planck waves towards a body that is slow ...
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How is Newtonian Mechanics contradictory to Special Relativity at a certain parameter? [duplicate]

How is Newtonian Mechanics contradictory to Special Relativity at a certain parameter and what conditions must be met for Newtonian Mechanics to be a suitable model for describing systems?
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Consequences of infinite speed of light [closed]

If an object is moving at infinite constant speed $v=\infty$, then it will cover an infinite distance $\Delta s=\infty$ (and so any distance) in any finite time $\Delta t<\infty$ v=\frac{\...
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Deriving the speed of light from Maxwell's equations?

Relationship between speed of light and EM force? Can it be said that Maxwell used measurements of the "strength of electric force and strength of magnetic force", to derive the value for the speed ...
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Would the Michelson-Morley Experiment have Discovered our Atmosphere?

We all know the earth is surrounded by an atmosphere, and we know that it is the medium through which sound travels. If the Michelson and Morley experiment was modified to find sound’s medium would ...
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Why are speeds of different EM waves in vacuum not EXACTLY equal?

It is said in my textbook (reference below) that the different waves of the Electromagnetic Spectrum have velocities almost equal to each other. (Variations are within a few m/s according to my ...
351 views

How was it determined that the speed of light in vacuum is a constant?

For over a hundred years now we have accepted that the speed of light is the same in all frames of reference. What I'm wondering is - how was this determined? I'm aware of the Michelson and Morley ...
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Is a light year a different distance if measured from a moving object?

The speed of light is absolute, but time is relative. So would a light-year for us on earth be a different distance from a light-year on a different uniformly moving object? Why or why not?
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What does it mean to SQUARE the speed of light? [closed]

$E=mc^2$ But what exactly does it MEAN to square the speed of light? Like, what is happening in the universe at that point in the equation?
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What happens when the speed of light is reached and the radius is reduced in angular motion? [closed]

If so that the angular momentum is conserved, when the radius is decreased it increases the speed, what happens when it reaches the speed of light and why does it not exceed it?
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Does the age of the universe depend on the speed of light?

In the Big Bang theory of the universe, does the value of the speed of light enter into the calculation that determines the age of the universe, and if yes, in which way?
181 views

Michelson-Morley Experiment as evidence for Special Relativity

Context: Our state (NSW, Australia) recently got a new syllabus for the year 12 physics course, and as such we are the first year going through with the new course. One of the things we need to learn ...
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Standard Definition of speed of light and metre

The speed of light is the speed at which lightwaves propagate through different materials. In particular, the value for the speed of light in a vacuum is now defined as exactly 299,792,458 metres per ...
52 views

Speed of a current passing through a wire [duplicate]

The wire is at 50hz, and is an aluminum alloy (AAAC 1120). Resistance in the wire is at 0.0897 ohm/km. So for a length of conductor 135km long, the resultant resistance will be 12.1095 ohm. It's AC ...
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How to beat speed of light using graphene pulley motor? [duplicate]

A 10 meter graphene pulley with 10,000 teeth, attached to a second graphene pulley of 10mm with 10 teeth both in a low temperature vacuum chamber. The first graphene pulley is being rotated by a ...
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Measuring Speed of Light with A Ruler in Expanding Space

At $t_0$, we have a ruler which has two tick marks (one at each end) with one labeled "$0$" and the other labeled "$L$" (it is $L$ units long). Suppose at that time we also have two point objects ...
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Newton's cradle faster than light? [closed]

If we have a Newton's cradle toy where the balls actually touch each other. Can energy be transferred from the first ball to the last one faster than the speed of light? And what factors control the ...
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Michelson-Morley's experiment - neglecting gravity?

Michelson and Morley's experiment, together with other experiments, was determinant to establish one of the postulates of Einstein's special relativity, namely that the speed of light is the same in ...
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When 'speed of light' changes, is it because the pendulum moves slower or the transition of caesium-133 gets more sluggish or?

I am a layman thinking about the speed of light. Say we measure the speed of light as: number of Bohr radii the light covers per pendulum swing number of Bohr radii the light covers per 9192631770 ...
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How did people estimate the speed of light before modern technology? [duplicate]

I just read a wikipedia page on the speed of light. Apparently people have made pretty accurate estimates for almost 200 years. How did they do this? How did they measure any fundamental constant ...
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On existence of mass in different form [closed]

(I'm a mathematician actually. This is my first question on this site. So please go easy on me if it's a trivial matter or mistake) Lately I've been thinking about special relativity. The thought ...
183 views

Why can't we define absolute rest?

If, according to the theory of relativity, as objects gain velocity and approach the speed of light then time for them slows down, why can't we define absolute rest as the inertial frame in which time ...
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Gravitational Time Dilation and Speed of Light [duplicate]

From what I'm understanding, the Speed of Light is roughly 186k MPS NO MATTER WHAT! Then say if a bean of light shoot pass near a Black Hole (Outside the Event Horizon of course) 1k lightyear away to ...
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Does the equivalence principle imply that light must move slower when moving away from a massive object?

Thought experiment: Elevator going up at an extreme acceleration, pulse of light bouncing up, and down between mirrors on the floor, and the ceiling. Won't it take light longer to travel from the ...
132 views

General “relativity” without special relativity

I was wondering if there could be a way of using the principle of equivalence and develop a theory of warped space-time without using special relativity, ie, without assuming any maximum possible ...
33 views

Red shift of radio signals

If a radio signal is red-shifted does it still last the same amount of time? Knowing the signal wavelength is now longer but still is traveling at the speed of light one would assume the radio message ...
93 views

How can light reach its speed? [duplicate]

The mass of a photon is said to be 0, But light (photons) get attracted due to gravity of a black hole, that means photons have a mass which is very very very small. And we know that any object with ...
143 views

Why can't gravity force an object past the speed of light? [duplicate]

I hope this question is not a duplicate (it doesn't seem to be) and that it is appropriate for this site. If we had a universe with only two bodies. One is ultra massive, and the other is very small. ...
3k views

Has the speed of light ever been measured in vacuum?

According to: https://en.wikipedia.org/wiki/Cosmic_microwave_background the CMB (Cosmic Microwave Background) "is faint cosmic background radiation filling all space" Also, https://en.wikipedia.org/...
125 views

Why I think the Michelson-Morley experiment was originally flawed, and would have failed either way [closed]

I was recently reading about how physicists were heavily relying on the existence of Luminiferous Aether for their physics to work. I read about how the Michelson-Morley experiment attempted to prove ...
199 views

Why can't we measure the one-way speed of light?

I believe the problem is because we need to synchronize clocks. But ok let's assume we can't do that. Can't we just use some external reference - Eg The Sun & Solar Noon? For example given the ...
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Doesn't the speed of light limit imply the same electron can be annihilated twice?

If I understand correctly, there is a small probability the same electron to be found anywhere in the universe. Suppose that an anti-electron collides with an electron, annihilating it and producing ...
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If light speed determines the rate of time, could the speed of light be varying over time and we be unaware of it?

Is this a valid implication/alternative explanation of universal red-shift? I thought I'd ask this when I read this question about light clocks. I had speculated this way: If light speed determines ...
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On the Rømer experiments and the speed of light

In 1676, Rømer determined that the speed of light must be finite. His experiment consisted on observing the eclipses of Io, one of Jupiter's moons, by Jupiter itself. He timed these eclipses over a ...
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Expansion of the universe – impossible for future astronauts to make it back

The universe is rapidly expanding. If future astronauts built a spaceship that could travel close to the speed of light and took off, there is a certain point where they could not make it back again ...
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What is $c$ in Gaussian Units?

Is the speed of light in Gaussian Units just 1 or can it be expressed in metric units? I am getting really confused by all the unit systems. In relativity, for instance, c is often set equal to 1 ...
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Is the observable universe equivalent to 'our' light cone?

All the objects we can observe (stars, galaxies, ...) must be in our past light cone, since otherwise we couldn't see them. Presumably there are more objects located outside of our observable universe ...
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Can massless particles change their quantum state? What about with entanglement?

It is well established that any massless particle, by special relativity, must travel at the speed of light, e.g. Special relativity and massless particles. Accordingly, this means that massless ...
73 views

Gravitational field of sun [closed]

Let there be a solar system without Earth. Now what happen if we place the Earth suddenly on its actual position does the gravitational force of sun acts on it immediately because of its pre ...
139 views

“Black hole spins at $X$% of the speed of light”, what does that mean?

I've seen a few news stories recently (example, example) about some black holes spinning at X% of the speed of light. What does that mean? What exactly is moving at that speed, and with respect to ...
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Why doesn't the energy of an incident photon impact the angle of reflection?

Note that I am not asking why the angle of reflection is what it is. That is a different question. I am asking why the energy of the incident photon does not affect the interaction in question at all,...
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High speed and low speed photons (hypothesis - difference/relation)

In this question I found an interesting answer with the source. Quotation: A telescope viewing a supernova from over 16 billion light years away recently clocked the low energy photon arriving 5-...
134 views

Relative speed when getting close to the speed of light

I was thinking about the relative speed of an observation reference frame and an object which has been accelerated to a speed close to the speed of light. I'm by no mean an expert and the last physics ...
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Two ships, one year apart, travelling from earth to a distant planet. What is the time difference of arrival? [closed]

If a ship set off at a significant percentage of the speed of light, and landed on a distant planet, and then a second ship set off a year or so later, what would the time distance be at the ...
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Increasing the view of observable universe

I have read that the maximum observable universe is about 92 billion light years in diameter by measuring the microwave background waves emitted after some few million years ago from the big bang and ...
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Law of cosines in Time dilation formula derivation [duplicate]

In my book, Bob takes off on a spaceship with a light clock so that the direction of motion of his spaceship is perpendicular to the direction of motion of light in the light clock. As a result, ...
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Does light emitted in opposite direction hit equally distant objects at different times?

I am a physics student just learning about special relativity for the first time, and was wondering what would happen if you emitted two photons of light from the center of a boxcar in opposite ...
I'd like to start off by saying this may be totally wrong; thus I would like some help clarifying this. Suppose you are in a vacuum, and a beam of light is travelling at, say, a N$45°$E bearing. The ...